Alkylation-dealkylation process



1952 B. B. coRsoN r-:T AL

ALKYLATIoN-DEALKYLATION PROCESS Filed Aug. 12, 1948 March 1 1 E n nzmu A Patented Mar. 11, 1952 UNITED STATES PATENT OFFICE Ben Bennett Corson and Walter M. Kutz, Pittsburgh, Pa., assignors to-Koppers Company, Inc., Pittsburgh, Pa., a corporation of Delaware Application August 12, 1948, Serial No. 43,908

This invention relates to processesl for effecting exchange reactions between alkylatable aromatic compounds and poly-substituted aromatic compounds at least one substituent of which is an alkyl group regeneratable as an olen, and is particularly directed to processes for obtaining monoethyl benzene from diethyl benzene.

This application is a, continuation in part of our copending application, Serial Number 620,810, led October 6, 1945, now abandoned.

It is known in the art that monoethyl benzene may be obtained from diethyl benzene by a disproportionation or exchange reaction. In reactions of this type a mixture of benzene and diethyl benzene is brought into contact with a suitable alkylating-dealkylating catalyst at a reactive temperature such that the diethyl benzene is partially dea-lkylated to yield monoethyl benzene. In this dealkylation ethylene is regenerated and immediately combines with the benzene to form a further amount of monoethyl benzene. The processes heretofore available for this purpose have suffered disadvantages in that both the yield per pass and the ultimate yield are low, in the formation of excessive quantities of gaseous by-productsl and carbon which reduce the ultimate yield and impair the activity of the catalyst, and in the formation of undersira-bly large amounts of polycyclic products.

It is an object of the present invention to avoid the disadvantages of the prior art and to provide dispro-portionation processes of an improved character generally applicable to eiiecting disproportionation reactions with polvsubstituted aromatic compounds at least one substituent of which is an alkyl group regeneratable as an olen. A particular object of the invention is to provide improved disproportionation processes which give substantially increased yields as compared with the prior art processes. Another particular object is to minimize the deposition of carbon and thereby prolong catalyst life. Still another object is to minimize the formation of gaseous ley-products and polycyclic by-products thereby to increase the ultimate yield. Further objects will appear as the description proceeds.

These objects are accomplished in the present invention by contacting a mixture containing a polysubstituted aromatic compound, at least one substituent of which is an alkyl group regeneratable as an olefin, and an alkylatable aromatic 23 Claims. (Cl. 2611-671) ating catalyst at a reactive temperature below about 450 C. and at the pressure-substantially above atmospheric. Under these conditions we are able to obtainhigh ultimate conversionof the polysubstituted aromatic `to alkylated aro?. matic, high conversion per pass,` very little carbon deposition and, consequently, prolonged catalyst life, and very little formation of undesir able by-products, particularly gases. .v j

In carrying out the processes of the invention, a mixture containing polysubstituted aromatic compound, at least one substituent of whichis an alkyl group which is regenerata-ble as an olefin, and an alkylatable aromatic compound in the proportions of at least 2.5 mols of alkylatable aromatic compound foreach mol product-equivalent of the polysubstituted aromatic compound is contacted continuously or batchwise with a suitable alkylating-dealkylating catalyst at a reactive temperature below about 450 C. while maintaining a pressure substantially above atmospheric, preferably between about 15 and about 60 atmospheres.

Disproportionation reactions of the type to which the invention relates may be represented in the following equation:

in which S is a substituted aromatic radical of valence n, n is an integer, R is an alkyl radical regeneratable as an olen, and ArI-I is an alkylatable aromatic compound. SRn, therefore, is the polysubstituted aromatic compound, at least one substituent of which is an alkyl group regeneratable as an olefin. It is the donor reagent. ArH is the acceptor reagent. As the donor reagent, SRm, gives n -l- 1 mols of product, nArR-i-SH, the expression n -l- 1 is the mol product equivalent of the donor reagent. Where diethyl benzene is the donor and benzene is the acceptor n equals 1 and the equation becomes 1 diethylbenzene-lbenzene- 2 ethylbenzene-l- 4 benzene By having present in the reaction mixture at least 2.5 mols of alkylatable aromatic compo-und f for each mol product-equivalent of the donor reagent there is always present a substantial excompound 'in the proportions of at least about 2.5

mols of alkylatable aromatic compound for eachH mol product-equivalent -of the npolysubstituted.. v aromatic compound with an alkylating-dealkylabove atmospheric makes it possible to attain recess of the acceptor reagent even if the reaction is carried substantially to completion. The use of this excess of alkylatable aromatic compound coupled with a -relatively low temperature, i. e., belowabout 450 C. and a pressure substantially pounds.

markably high ultimate yields and remarkably high yields per pass, and at the same time to obtain a marked reduction in the amount of carbon formation and other by-products such as gases and polycyclics as compared with the prior art processes.

The disproportionation reactions to which the invention is directed are not to be confused with the disproportionation of Xylene and benzene. When a mixture of xylene and benzene is subjected to a suitable dealkylating-alkylating catalyst under suitable conditions an exchange or disproportionation reaction takes place. However, the mechanism of this reaction is entirely different from that illustrated in the above equations because it is not possible in the dealkylation of xylene to regenerate an olefin. Rather, it is necessary to effect an interchange between methyl radical and a hydrogen of the benzene. Possibly a free methylene radical splits 01T. and reacts with the benzene; but whatever takes place, the reaction is so unlike that which takes place where the alkyl group is capable of regenerating an oleiin that entirely different conditions `are required and differentby-products result. See Hansford et al., Industrial and Engineering Chemistry, vol. 37, pages 671-5 (1945).

The disproportionation reactions according to the invention may be considered as a combined dealkylation and alkylation in which the olefin used in the alkylation is generated in the dealkylation. What is required to effect this kind of disproportionation is a polysubstituted aromatic compound at least one substituent of which is an alkyl group regeneratable as an olen capable to act as the donor reagent and an alkylatabler aromatic compound to act as the acceptor. To act as an acceptor in the reaction the aromatic compound should have an affinity for the olefin greater than the dealkylation product of the donor reagent; otherwise, this product would be realkylated in preference to the acceptor reagent. Thus, by alkylatable aromatic compound we mean an aromatic compound having sufficient affinity for olen toact as an acceptor in the disproportionation reaction. The invention is therefore applicable to awide variety of donor andacceptor reagents. The donor reagent, for example, may ,be dior tri-ethylbenzene, dior tri-ethylnaphthalene, the mono and diethyl phenols and the corresponding isopropyl and tertiary butyl com- Suitable acceptors include benzene, 'naphthalena phenol and toluene. While these donors and acceptors may be used in any combination, it is desirable so to select them that the products of the dealkylation and the alkylation are identical; for example, a combination of dior tri-ethyl benzene with benzene, etc., that is to say, a combination of disubstituted aromatic compound'with the corresponding aromatic compoundiasacceptor.

The invention may be more fully understood by reference to the accompanying flow sheet illustrating diagrammatically apparatus suitable for carrying out a process of the invention. Benzene and polyalkylbenzene are introduced into receiver I in the correct proportions and the mixture is pumped by pump 2 through heater 3 into catalytic reactor 4. The catalysate passes into a high pressure receiver 5. Nitrogen is pumped into high pressure receiver 5 by pump 6 as required to maintain the desired pressure in the catalytic reactor. The catalysate is withdrawn from the high pressure receiver 5 into low pressure receiver 1 through reducing valve 8 and condenser 9. Nitrogen is vented through vent I0 and the liquid product is passed through line I I into a primary distillation column I2. Benzene, taken off as overhead, is condensed in condenser I3 and returned to receiver I through line I4. The bottoms, which consists essentially of a mixture of monoand polyalkylbenzenes, is passed through line I5 into a secondary distillation column I6. The bottoms of the secondary, which consists essentially of polyalkylbenzene, is passed through line I'I to receiver I. The overhead, consisting essentially of rnonoalkylbenzene, is condensed in condenser I8 and recovered as the product of the process.

The following examples will serve to illustrate typical operations according to the invention. The parts are by weight and the pressure is gauge unless otherwise specified. The catalyst was prepared as follows:

Silica gel was precipitated from dilute aqueous water-glass by hydrochloric acid and washed with distilled water until the sodium content of the gel was lowered to about 0.1%. The freshly prepared washed silica gel was dispersed in dilute aqueous aluminum chloride and aqueous ammonia was added with stirring. The intimate mixture of silica and alumina gels thus obtained was thoroughly washed with distilled water and dried at C. The dried product contained about 10% alumina and the balance silica. The dried product was crushed, screened to 20-30 mesh and pelleted in the form of 1/8 inch x 1/8 inch pellets using 4% of aluminum stearate as a die lubricant. The pellets were heated in a stream of air at 600 C. to remove organic material before use as the catalyst. l

EXAMPLE I A mixture of benzene and diethylbenzene in the proportions indicated in the following table was passed over the above catalyst at a tempel'- ature of 400 C. at a pressure of 500 lbs. per square inch and at a liquid hourly space velocity of 2; i. e., 2 volumes of liquid per hour per volume of catalyst. The following table illustrates the results obtained:

It is significant to note that both the yield per pass and the ultimate yield markedly increased as the proportion of benzene was increased from 5 to 15 mols for each mol of diethyl benzene. The significance of these figures may be more fully realized by comparing them with results obtained by others who have carried outa disproportion reaction between benzene and diethyl benzene. This comparison is shown in Table II.

Table 1I 10 Weight Yield Per cent on Diethylbenzene charged Theoretical Yield Per cent of Maximum Possible Yield Procedure Per Pass Ultimate Per Pass Ulti mate From these data it will be observed that the ylelds obtained by the processes of the invention are markedly superior to those obtained by the indicated investigators. It is particularly significant to note that'under the preferred operating conditions according to the invention; i. e., between about 10:1 and 15:1 ratios the yields per pass obtained, according to the invention, are of .the same magnitude as the ultimate yields obtained in the prior art.

The advantages of the processes of the inventionare further illustrated in the data given in Table III in which the amount of carbon deposited on the catalyst and amount of gaseous products formed in processes of the invention is compared with the results obtained by other investigators.

Table III v Gaseous Products .Per cent of Charge Carbon Deposited on Catalyst Per cent of Charge Example I:

10:1 m01 ratio U. S. Patent 2,389,445:

Ratio-3:1 Temp-600 C Pressure-Atmospheric Space Velocity-0.5.... Hansford supra:

, ao-3:1 Temp-454 C. and u p 5 Pressure-Atmospheric Space Velocity1.l0

Less than 0.03

Example I in which a 10:1 mol ratio was used was regenerated by heating it in a stream of air at 600 C. for 3 hours. The regenerated catalyst under the same conditions of the example gave a somewhat higher conversion per pass during the rst twelve hours than the fresh catalyst, the conversion falling from 55% during the rst twelve hours to 32.5% during the third twelve hours. The average conversion per pass over the 36-hour period was 42% and the average ultimate yield was 92%.

EXAMPLE III A mixture of 1728 parts of benzene and 359 parts of di-isopropylbenzene was heated to a temperature of 400 C. and passed over catalyst prepared as in Example I at the same temperature at a liquid hourly space velocity of two. The mol r'atio of benzene to di-ieopropylbenzene was ten. After distilling off the benzene, the product analyzed 419 parts mono-isopropylbenzene, 42 parts di-isopropylbenzene and 24 parts higher boiling constituents. The yield of mono-isovpropylbenzene per pass was 79% and the ultimate yield was 89%.

In place of benzene and di-isopropylbenzene, there may be substituted naphthalene and di-isopropylnaphthalene.

While the invention has been described with reference to particular embodiment thereof, it will be understood that variation may be made therein without departing from the spirit and scope of the invention as long as a mixture of polysubstituted aromatic compound an alkyl group of which is regeneratable as an oleiin and an alkylatable aromatic compound in the proportions of at least 2.5 mols of the alkylatable aromatic compound for each mol product equivalent of the polysubstituted aromatic compound is contacted with an alkylation-dealkylation catalyst at a reactive temperature below about 450 C. and at a pressure substantially above atmospheric pressure.

The processes of the invention require a catalyst to effect the dealkylation and the realkylation. In general, any catalyst by which an aromatic compound may be alkylated by means of an olefin may be used. Catalysts which comprise precipitated silica on one or more refractory oxides as described in U. S. Patent 2,389,445 may be used. Similarly, catalysts containing Various combinations of silica and alumina, whether prepared synthetically or obtained by the treatment of natural products, such, for example, as disclosed and described in U. S. Patents 2,222,632; 2,366,217; 2,115,884; 2,282,922; 2,287,917; 2,329,- 307; 2,242,553; 2,270,090; 2,285,314 and 2,229,353 may be used.

The optimum temperature for continuous operation is about 400 C. although satisfactory conversions may be obtained between about 350 C. and about 450 C. In batch operation lower temperatures, e. g., 250 C. or less, may be used in view of the increased contact time. At lower temperatures the conversion per pass falls off rapidly and at higher temperatures the life of the catalyst and its capacity of being regenerated is impaired by deposition of carbonaceous material as the result of destructive cracking.

The optimum proportions require at least about 5'.mols of aromatic compound for each monolalkyl aromatic equivalent'although satisfactory results may be obtained with as little as 2.5 mols. Still greater excesses of benzene may be utilized Vbut for practical purposes it will rarely be neces 7 sary or desirable to use vmorethan about 7.5 mols per' monoalkyl aromatic equivalent.

The optimum pressure is in the order of 500 pounds per square inch. Higher pressures may be used but excessive pressure tends to reduce yields. For example, at 900 pounds per square inch the yields were slightly lower than at 500 pounds per square inch. When the pressure is too low, the yields drop off rapidly. Thus at 250 pounds per square inch, the conversion per pass was observed to be only about half that at 500 pounds per square inch. Between 250 pounds per square inch and atmospheric pressure the con- Version was observed to fall off to an insignificant figure. For example, the conversion per pass at atmospheric pressure was observed to be only one-sixteenth of the conversion per pass at 500 pounds per square inch. These comparisons were made on the basis of a liquid hourly space velocity of two which means that the contact time was shorter for the lower pressures. While this may account in part at least for the difference in the observed yields, it fails to account for the fact that they amount of carbon deposited on the catalyst was about the same or, if anything, greater at the lower pressures notwithstanding the shorter contact time. The net result is that the quantity of carbon deposited on the catalyst per unit production of monoalkyl aromatic compound is far greater at atmospheric pressure. For example, operating at atmospheric pressure the amount of carbon deposited upon the catalyst per unit production of monoethylbenzene was observed to be about nines times that deposited at 250 pounds per square inch and about twenty times that deposited at 500 pounds per square inch. Operation at superatmospheric pressure therefore has the advantages of increased yield per pass and lower carbon formation per unit production of monoalkyl aromatic compound. The new effect of operating at superatmospheric pressure therefore is to extend the catalyst life per unit production of monoalkyl aromatic compound.

In continuous operation the optimum liquid hourly space velocity is about two. At lower space velocities the conversion per pass is somewhat higher but not enough so to compensate for loss in throughput. The ultimate yield is about the same. pass tends to drop off slightly. Liquid hourly space velocities between one and ve should vbe suitable. The invention in its broader aspects, however, is not limited to any particular space velocity since this may vary with the design of the apparatus and the activity of the catalyst. Those skilled in the art, in view of the foregoing, will suitably be able to adjust the throughput to obtain optimum performance.

We claim:

1. In a process for effecting the transfer of an alkyl group from one aromatic nucleus to another in which the donor reagent is a polysubstituted aromatic compound at least one substituent of which is an alkyl group regeneratable as an olefin and the acceptor reagent is an alkylatable aromatic compound, and in which the transfer is effected by subjecting a mixture of the donor and acceptor reagents to catalysis over an alkylating-dealkylation catalyst, the steps of bringing a mixture of the donor and acceptor reagents which yield the same product through dealkylation of the donor reagent and alkylation of the acceptor reagent and in which the proportions are at least two and one-half mols of acceptor At higher space velocities the yield per reagent for'each mol product equivalent of the donor reagent in contact with said catalyst at a reactive temperature below about 450 C. while maintaining a pressure between about 15 and 60 atmospheres.

2. The process of claim 1 in which the catalyst is a silica-alumina catalyst.

3. The process of claim 2 in which the alkyl group of the donor reagent contains less than 5 carbon atoms.

4. The process of claim 3 in which the acceptor is benzene.

5. `The process of claim 4 in which the alkyl group regeneratable as olefin is ethyl.

6. The process of claim 5 in which the donor reagent is diethylbenzene.

7. TheZ process of claim 6 in which the temperature is between about 250 C. and about 450 C. and the space velocity is between about 1 and about 5. l v

8. The process of claim 7 in which the proportions are between about 5 and about 7.5 mols of 'acceptor reagent for each m01 product equivalent of the donor reagent.

9. The process of claim 1 in which the alkyl group regeneratable as an olelin is isopropyl.

10. The process of claim 9 in which the catalyst is a silica-alumina catalyst.

11. The process of claim 10 in which the acceptor and donor reagents yield the same product through alkylation of the acceptor reagent and dealkylation of the donor reagent.

12. The process of claim 11 in which the acceptor is benzene.

13. The process of claim 12 in which the donor reagent is diisopropyl benzene.

14. The process of claim 13 in which the temperature is between about 250 C. and about 450 C. and the space velocity is between about l and about 5.

15. The process of claim 14 in which the proportions are between about 5 and about '7.5 mols of acceptor reagent for each mol product equivalent of the donor reagent.

16. In a process for effecting the transfer of an alkyl group from one aromatic nucleus to another in which the donor reagent is a polysubstituted aromatic compound at least one substituent of which is an alkyl group regeneratable as an olefin and the acceptor reagent is an alkylatable Aaromatic compound, and in which the transfer is effected by subjecting a mixture of the donor and acceptor reagents to catalysis over an alumina-silica catalyst, the steps of bringing a mixture of the donor' and acceptor reagents which yield the same product through dealkylation of the donor reagent and alkylation of the acceptor reagent and in which the proportions are at least 2.5 mols of acceptor reagent for each molv product equivalent of the donor reagent into contact said catalyst at a reactive temperature below about 450 C. while maintaining a pressure between about 15 and about 60 atmospheres.

17. The process of claim 16 in which the acceptor is naphthalene.

18. The process of claim 16 in which the acceptor is benzene.

19. vThe process of claim 18 in which the donor is diethylbenzene.

20. The process of claim 16 in which the acceptor is benzeneand the donor is di-isopropylbenzene.

21. In a process for effecting the transfe of an alkyl'gro'up from one aromatic nucleus to another 4in which the donor reagent is 'a polyfsubstituted aromatic compound at least one substituent of which is an alkyl group which is regeneratablel as an olen and the acceptor reagent is an alkylatable aromatic compound, and in which the transfer is eiected by subjecting a mixture of the donor and acceptor reagents to catalysis over an alkylating-dealkylation catalyst, the steps of bringing into contact with said catalyst at a reactive temperature below about 450 C. while maintaining a pressure between about 15 and 60 atmospheres a mixture of said donor and acceptor reagents in the proportions of at least 21/2 moles of acceptor reagent for each mole product equivalent of the donor reagent, continuing said contact under the said conditions untl a substantial portion of said donor reagent is dealkylated and a corresponding amount of said acceptor reagent is alkylated, and recovering the products of said dealkylation and said alkylation.

22. The process of claim 21 in which the temperature is about 400 C.

23. The process of claim 21 in which the alkyl l0 group of the donor reagent contains less than 5 carbon atoms.

BEN BENNETT CORSON. WALTER M. KUTZ.

REFERENCES CITED The following references are of record in the e of this patent:

UNITED STATES PATENTS OTHER REFERENCES Hansford et al.: Industrial and Engineering Chem., July (1945), pages 671-675.

Natanson et al.: J. Phys. Chem. (U. S. `S. RJ, vol. 17, page 381 (1943). 

1. IN A PROCESS FOR EFFECTING THE TRANSFER OF AN ALKYL GROUP FROM ONE AROMATIC NUCLEUS TO ANOTHER IN WHICH THE DONOR REAGENT IS A POLYSUBSTITUTED AROMATIC COMPOUND AT LEAST ONE SUBSTITUENT OF WHICH IS AN ALKYL GROUP REGENERATABLE AS AN OLEFIN AND THE ACCEPTOR REAGENT IS AN ALKYLATABLE AROMATIC COMPOUND, AND IN WHICH THE TRANSFER IS EFFECTED BY SUBJECTING A MIXTURE OF THE DONOR AND ACCEPTOR REAGENTS TO CATALYSIS OVER AN ALKYLATING-DEALKYLATION CATALYST, THE STEPS OF BRINGING A MIXTURE OF THE DONOR AND ACCEPTOR REAGENTS WHICH YIELD THE SAME PRODUCT THROUGH DEALKYLATION OF THE DONOR REAGENT AND ALKYLATION OF THE ACCEPTOR REAGENT AND IN WHICH THE PROPORTIONS ARE AT LEAST TWO AND ONE-HALF MOLS OF ACCEPTOR REGENT FOR EACH MOL PRODUCT EQUIVALENT OF THE DONOR REAGENT IN CONTACT WITH SAID CATALYST AT A REACTIVE TEMPERATURE BELOW ABOUT 450* C. WHILE MAINTAINING A PRESSURE BETWEEN ABOUT 15 AND 60 ATMOSPHERES. 